Fluoropolymer laminates and a process for manufacture thereof

ABSTRACT

The present invention provides fluoropolymer laminates having isotropic properties. For example, an embodiment in which multiple fluoropolymer sheets having an liquid crystalline polymer oriented in the fibrous state in the melt processible fluoropolymer are laminated, despite having the fibrous LCP oriented in one direction in each single extruded sheet, makes it possible to laminate in such a way as to compensate for their orientation directions, the laminate thereby becoming isotropic as regards physical properties. The laminates also have low linear coefficient of expansion and low thermal shrinkage as well as elevated tensile modulus and low dielectric constant.

FIELD OF THE INVENTION

[0001] This invention is in the field of fluoropolymer laminates.

BACKGROUND OF THE INVENTION

[0002] With trends toward miniaturization of devices, higherperformance, and greater circuit density in electrical and electronicparts fields, there is a need for materials with excellent heatresistance, dimensional stability, low moisture absorption, and lowdissipation at high frequencies, which is associated with dielectricconstant. In particular, as advancements are made in informationtechnology, circuit boards increasingly need to have good performancehigh frequency.

[0003] Circuit boards are commonly made from copper cladding on suchreinforcing substrates as follows: glass cloth impregnated with epoxyresin, fluoropolymer film, substrates obtained by impregnation of glasscloth with a liquid in which a polytetrafluoroethylene (PTFE) particlesare dispersed as disclosed in Japanese Patent Application PublicationKokai 2001-171038, and laminates obtained by laminating polyphenylenesulfide (PPS) film to a fibrous product mainly comprised of PTFE asdisclosed in Japanese Patent No. 3139515.

[0004] However, these films and laminates are deficient in the followingaspects: Copper-clad laminates obtained by impregnation of glass clothwith an epoxy resin are inferior in high frequency characteristics andmoisture absorption characteristics, and they often warp, which isattributable to the differences in the coefficient of thermal expansionof the substrate and the copper foil. Furthermore, they sometimes sufferfrom an inability to accept plating (copper cladding) when the glass isexposed in the through holes. Through-holes are holes made though thecircuit board, the inside of the holes being metal-plated to provide anelectrically conductive connection between layers in the board.Copper-clad fluoropolymer laminates also tend to suffer from thermalstress due to the differences in the coefficients of thermal expansionof the copper foil and the fluoropolymer substrate, resulting inproblems such as the delamination of the copper foil. Fluorinated filmsubstrates are not easily adhered to: they have difficulty acceptingpaste and plating during the printing for a circuit formation,lamination of metal foils, or through-hole fabrication. Laminates fromPTFE fibrous product and PPS film, while showing low thermal shrinkage,are inferior in high frequency characteristics due to the use of the PPSfilm, which has a dielectric constant higher than that of thefluoropolymer.

[0005] Liquid crystalline polymers (LCP) would be expected to findapplications in electronic parts areas because of their high strength,high heat resistance, low coefficient of thermal expansion, and goodinsulation characteristics. It has been disclosed that blending a meltprocessible fluoropolymer with an LCP and causing the LCP to be in afibrous state in the melt processible fluoropolymer matrix can improvethe tensile modulus of the melt processible fluoropolymer and itscoefficient of linear expansion (EP 1 086 987 A1). It has also beendisclosed that introduction of a fluoropolymer having a specificfunctional group (hereafter called a compatibilizing agent) brings aboutuniformity in the size of the LCP dispersed phase and dispersion statein the melt mixing stage of the fluoropolymer and the LCP and improvesthe interfacial adhesion between the fluoropolymer and the fibrous LCPU.S. patent application Publication 2001/0006727). However, thesefluoropolymer-liquid crystal polymer blends have failed to providereliable electronic materials and products because during meltextrusion, the LCP molecules extensively orient in the direction ofextrusion (machine direction). As a result, the resulting films arehighly anisotropic, exhibiting differences in tensile strength andcoefficient of linear expansion between the machine direction (MD, thedirection in which the LCP fibers are oriented) and the transversedirection (TD, the direction perpendicular to the direction in which theLCP fibers are oriented. In extruded film or sheet, TD is the width ofthe extrudate.).

[0006] These shortcomings have prompted a proposal for a processcomprising laminating porous fluoropolymer films to both sides of apreviously-extruded LCP film, stretching the laminate biaxially undertemperature conditions where the porous fluoropolymer is not melted, butwhere the LCP is melted, thereby reducing or eliminating the anisotropyso as to be able to use the LCP as a circuit substrate material (KokaiH10-34742). This approach is alleged to cause the LCP molecules to berandomly orientated in the plane of the laminate, thereby reducing oreliminating anisotropy in the physical properties. However, unlikeconventional thermoplastic polymers, LCPs have rigid molecular chainswhich tend to slip past one another with essentially no entanglementbetween individual molecular chains, making it comparatively difficultto stretch them at a temperatures below their melting points. Attemperatures at or above their melting points, the viscosities of LCPsdrop precipitously; and they flow like liquid thereby losing allfibrillar orientation. Therefore, fibrous LCP is very difficult toorient completely randomly, even when the LCP is laminated betweenporous fluoropolymer films and biaxially stretched.

[0007] There is a need for circuit board material that is free fromprior art defects.

SUMMARY OF THE INVENTION

[0008] It is an object of this invention to provide a melt processiblefluoropolymer laminate which exhibits high mechanical strength, a lowcoefficient of linear expansion and low thermal shrinkage by having aliquid crystalline polymer (LCP) present in the fibrous state in thefluoropolymer matrix, while retaining the excellent heat resistance, lowmoisture absorption, and high dielectric characteristics of thefluoropolymer and LCP, and which is suitable for circuit boards byvirtue of elimination of anisotropy in these physical properties. It isanother object of this invention to provide a melt processiblefluoropolymer laminate suitable for circuit boards which enables copperfoil to be laminated without use of adhesives by using a compatibilizingagent along with the LCP.

[0009] One of the preferred embodiments is a fluoropolymer laminatecomprising at least two fluoropolymer sheet layers, each having an LCPoriented in the fibrous state in the melt processible fluoropolymer,wherein said at least two layers have their respective fibrous LCPoriented in different directions from each other. This lamination of thetwo sheets with different orientation directions of the fibrous LCPcontained in each sheet balances the orientation effects of the fibrousLCP in the different directions of orientation. When the differentdirections of orientation are perpendicular to one another, the laminateis isotropic in these perpendicular directions. If anisotropy isacceptable, then the laminate can comprise as little as one sheet layerof the melt processible fluoropolymer containing the LCP oriented in thefibrous state, such laminate including copper cladding adhered to atleast one side of the sheet layer.

[0010] A further preferred embodiment includes a fluoropolymer laminatecomprising melt processible fluoropolymer layers wherein thefluoropolymer sheet layer having an LCP oriented in the fibrous state inthe melt processible fluoropolymer is a fibrous sheet layer selectedfrom the group consisting of woven fabric, non-woven fabric, and knittedfabric of melt processible fluoropolymer fibers containing the LCPoriented in the fibrous state in the fiber direction. To this fibroussheet, a melt processible fluoropolymer sheet containing no fibrous LCPcan be laminated to at least one side of said fibrous sheet.

[0011] The expression “oriented in the fibrous state” and the like meansthat the LCP is in the form of discontinuous fibers dispersed in thefluoropolymer matrix, whether the matrix is in the form of a filmforming the sheet or in the form of filaments from which the fibroussheet embodiment is made. The orientation of these fibers means thatthey are aligned in one direction. In the case when the sheet is anextruded film of the fluoropolymer, the alignment is in the direction ofextrusion. In the case when the sheet is a fibrous sheet, the alignmentis in the direction of melt spinning of the filaments from which thesheet is made. Since the filaments, including yams made therefrom,generally run in perpendicular directions, the fibrous sheet embodimentwill be balanced (isotropic) in these directions. Consequently, aslittle as a single fibrous sheet can be used to form an isotropicreinforcing substrate for copper cladding.

[0012] It is preferred for fluoropolymer sheet layer having an LCPoriented in the fibrous state in the foregoing melt processiblefluoropolymer to have the LCP formulated therein at a rate of about3-30% by weight thereof, preferably about 3-25 wt %.

[0013] A further preferred embodiment of the invention includes afluoropolymer laminate wherein the fluoropolymer sheet layer in which anLCP is oriented in the fibrous state in the melt processiblefluoropolymer is laminated to at least one side of a polymer layer witha coefficient of linear expansion of about 6×10⁻⁵/° C. or less. Thisembodiment provides a preparative advantage in that even when two sidesof the melt processible fluoropolymer layers have fibrous LCPs whoseorientation directions are the same, no substantial anisotropy expansionis seen, thereby making it unnecessary to consider the orientationdirection.

[0014] Preferred from among the foregoing fluoropolymer laminates of thepresent invention is one having a thermal shrinkage at after exposure to250° C. of not more than about 1.5% and a dielectric constant at thefrequency 1 GHz of not more than about 3.0.

[0015] The present invention also provides a process for the manufactureof a fluoropolymer laminate, which process comprises melt mixing a meltprocessible fluoropolymer with an LCP having a melting point of at leastabout 10° C. higher, preferably least about 15° C. higher than that ofsaid melt processible fluoropolymer; extruding the resultant meltmixture in the form of a sheet in which the LCP is oriented in thefibrous state in the melt processible fluoropolymer in the direction ofsaid extruding; overlapping multiple sheets obtained from said extrudingin such a way at least two of said sheets have their respective LCPoriented in the fibrous state oriented in different directions; andlaminating said multiple sheets together. This lamination usuallyinvolves subjecting the assemblage of overlaid sheets to heat andpressure that bonds them to one another.

[0016] The present invention further provides a process for themanufacture of a fluoropolymer laminate, which process comprisesoverlaying a melt processible fluoropolymer sheet containing no fibrousLCP on at least one side of a fibrous sheet selected from a wovenfabric, a non-woven fabric, or a knitted fabric of fluoropolymer fibershaving an LCP oriented in the fibrous state in the melt processiblefluoropolymer in the fiber direction; and laminating them together. Asabove, heat and pressure can be used to achieve this lamination.

[0017] The present invention further provides a process for themanufacture of a fluoropolymer laminate, which process comprises meltmixing a melt processible fluoropolymer with an LCP having a meltingpoint of at least about 15° C. higher than that of said melt processiblefluoropolymer; extruding the resultant melt mixture in the form of asheet in which the LCP is oriented in the fibrous state in the meltprocessible fluoropolymer; overlaying at least one sheet obtained fromsaid extruding on at least one side of the isotropic polymer sheet witha coefficient of linear expansion of about 6×10⁻⁵/° C. or less; andlaminating said fluoropolymer sheet and said polymer sheet together,such as by using heat and pressure as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a micrograph of the cleaved surface of a meltprocessible fluoropolymer sheet obtained in Example B.

[0019]FIG. 2 is a micrograph of the cleaved surface of a meltprocessible fluoropolymer sheet from Example C. These micrographs are ata magnification of 400×.

DETAILED DESCRIPTION

[0020] In this invention, conventional molding grade melt processiblefluoropolymer may be used as the melt processible fluoropolymercomponent, but it is preferred to use melt processible fluoropolymerhaving functional groups or a blend thereof with a conventional meltprocessible fluoropolymer.

[0021] Melt processible fluoropolymners in general use for molding areknown in the art, such as melt processible homopolymers and copolymers(copolymers being defined as polymers containing repeat units derivedfrom two or more monomers) of perfluoroolefin, fluoroolefin,fluorochloroolefin, fluoroolefin containing an ether group or acopolymer of one or more of these with ethylene. Examples of suchmonomers are tetrafluoroethylene, chlorotrifluoroethylene,hexafluoropropylene, perfluoro(alkyl vinyl ether), vinylidene fluoride,and vinyl fluoride.

[0022] Examples of such polymers are copolymer of tetrafluoroethylenewith one or more perfluoro(alkyl vinyl ethers) (hereafter PFA),tetrafluoroethylene/hexafluoropropylene copolymer (FEP),tetrafluoroethyelene/hexafluoropropylene/perfluoro(alkyl vinyl ether)copolymer (EPE), tetrafluoroethylene/ethylene copolymer (ETFE),polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), andchlorotrifluoroethylene/ethylene copolymer (ECTFE).

[0023] As for the melt processible fluoropolymers containing functionalgroups (also called functional group-containing fluoropolymers,) thefunctional groups include carboxyl and its derivatives, hydroxyl,nitrile, cyanato, carbamoyloxy, phosphonoxy, halophosphonoxy, sulfonicacid, or its derivative, and sulfohalides. Such functionalgroup-containing fluoropolymers act as compatibilizing agents, and arenormally blended with a conventional melt processible fluoropolymer suchas described above at concentrations that do not significantly affectthe conventional polymer's properties adversely. The functionalgroup-containing fluoropolymers are prepared, for example, bysynthesizing a melt processible fluoropolymer such as described aboveand then grafting these functional groups on to the polymer.Alternatively, functional groups may be incorporated by including in thecopolymerization a monomer having functional groups.

[0024] Specific examples of functional groups include —COOH, —CH₂COOH,—COOCH₃, —CONH₂, —OH, —CH₂OH, —CN, —CH₂O(CO)NH₂, —CH₂OCN,—CH₂OP(O)(OH)₂, —CH₂OP(O)Cl₂, and —SO₂F. These functional groups arepreferably introduced into the fluoropolymer by copolymerization.

[0025] Fluorine-containing monomers suitable for copolymerization andhaving such functional groups include, for example, fluorinated vinylether compounds represented by the formulas:CF₂═CF[OCF₂CF(CF₃)]_(m)—O—(CF₂)_(n)—X (where m is 0-3; n is 0-4, X is—COOH, —CH₂COOH, —COOCH₃, —CH₂OH, —CN, —CH₂O(CO)NH₂, —CH₂OCN,—CH₂OP(O)OH)₂, —CH₂OP(O)Cl₂, and —SO₂F. Most preferred are suchfunctional group-containing fluorinated vinyl ethers such as thoserepresented by the formula CF₂═CF—O—CF₂CF₂—SO₂F, orCF₂═CF[OCF₂CF(CF₃)]O(CF₂)₂—Y, where Y represents —SO₂F, —CN, —COOH,—COOCH₃ among others) or those represented by the formulaCF₂═CF[OCF₂CF(CF₃)]O(CF₂)₂—CH₂—Z (where Z represents —COOH, —OH, —OCN,—OP(O)OH)₂, —OP(O)Cl₂, and —O(CO)NH₂.

[0026] The grafting of functional groups onto fluoropolymers and theabove described fluorine-containing monomers are described further inthe patent literature.

[0027] These functional group-containing monomers should be present inthe functional group-containing fluoropolymers at concentrations ofabout 0.5-10% by weight, preferably about 1-5% by weight, based on thetotal weight of the fluoropolymer. If the functional group-containingmonomer content is too small in the functional group-containingfluoropolymer, the polymer's effect as a compatibilizing agent will besmall; having too great a content may result in strong interpolymerinteractions among the functional groups, resulting in an abruptincrease in viscosity to the extent that melt processing becomesdifficult. Furthermore, as the functional group-containing monomercontent increases, the functional group-containing fluoropolymer willbegin to have inferior heat resistance.

[0028] The functional group-containing fluoropolymers are notparticularly limited as to viscosity or molecular weight, but theyshould be melt processible and, if blended with conventional meltprocessible fluoropolymer, be similar in viscosity to the conventionalmelt processible fluoropolymer. Melt flow rate (MFR) should range fromno less than about 0.5, preferably about 1, more preferably about 2,most preferably about 5, to no more than about 100, preferably about 50,more preferably about 30, most preferably about 25. MFR is measured ing/10 min of molten polymer flowing through an orifice in accordance withthe procedure and equipment disclosed in ASTM 1238-94a and the ASTMprocedure applicable to particular fluoropolymers, e.g. ASTM D 2116-91a,ASTM D 3159-91a, ASTM D 3222-99, and ASTM D 3307-93.

[0029] The liquid crystalline polymer (LCP) used in this invention is athermoplastic resin which exhibits thermotropic liquid crystals, with noparticular limitation as to the melting point as long as there is noproblem in heat resistance at the melt processing temperature. However,in terms of processibility and heat stability, it is preferred to use anLCP having a melting point at least about 15° C. higher than that of themelt processible fluoropolymer. Such LCPs include polyesters, polyesteramides, polyester imides, and polyester urethanes; polyesters beingpreferred. Typical liquid crystalline polyesters are all-aromaticpolyesters. Many are known. They are derived from aromatic dicarboxylicacids and aromatic dihydroxy compounds or from aromatic hydroxycarboxylic acids, and may include polymerization units derived from analiphatic dicarboxylic acid, an aliphatic dihydroxy compound, analiphatic hydroxy carboxylic acid. In addition there are those havingpolymerizable units derived from aromatic dicarboxylic acids such asterephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid,and aromatic dihydroxy compounds such as hydroquinone, resorcinol,2,6-dihydroxy naphthalene, bisphenol A, dihydroxy diphenyl, and aromatichydroxy carboxylic acids such as para-hydroxy benzoic acid. LCP that canbe used in the present invention are further described in the patentliterature.

[0030] One of the methods for manufacture of a fluoropolymer sheetcontaining fibrous LCP is to melt blend melt processible fluoropolymerwith LCP, preferably along with said functional-group containingfluoropolymer and to extrude this blend into sheet form or as filamentsunder suitable conditions. The amount of functional group-containingfluoropolymer (compatibilizing agent) will depend on the type and amountof the functional group used, but should be about 0.5-30% by weight,preferably about 1-15% by weight of the above polymer material. Weightpercents are based on the total weight of the blend of fluoropolymer,including compatiblizer and LCP. The greater the amount of thecompatibilizing agent in the blend, the lower will be the surfacetension between the fluoropolymer and the LCP. Thereby, the interfacialadhesion will be greater. However, compounding too much functionalgroup-containing fluoropolymer may result in strong interpolymerinteraction among the functional groups resulting in an abrupt increasein the viscosity, sometimes making it difficult to melt process. Inaddition, an excessively high functional group-containing fluoropolymercontent will result in reduced heat resistance of the fluoropolymersheet.

[0031] The term “sheet” in this invention means broadly any article inwhich two of the dimensions (length and width) are significantly greaterthan the third (thickness) such as films, woven fabrics, non-wovenfabrics, and knitted fabrics.

[0032] The amount of LCP blended in the fluoropolymer should be about3-30% by weight, preferably about 3-25% by weight, and more preferably,about 4-25 wt %, based on the total weight of the blend Too little LCPwill not afford a sufficiently high reinforcing effect. Too much LCP inthe blend will risk having at least some of the LCP form large pocketsin the fluoropolymer matrix causing sudden local decreases in viscosityduring sheet extrusion steps, adversely affecting the uniformity thesheet or filament thickness. The LCP should not form the continuousphase, with the fluoropolymer dispersed therein.

[0033] The above functional group-containing fluoropolymer(compatibilizing agent) and the LCP each provide improved adhesion tometals such as copper, so that adjustment of the amount of each addedcan provide a laminate suitable for electrical and electronic partsapplications.

[0034] The mixing of the melt processible fluoropolymer andfunctional-group containing fluoropolymer with a LCP to provide thestarting material for the above fluoropolymer sheet can be done by anyconventional melt mixing method, but it is preferred to use an extruder,preferably one with a high shear rate, because high shear will betterdisperse the LCP, that is, distribute it in smaller particles throughoutthe fluoropolymer matrix. It is further preferred to use a twin screwextruder rather than a single screw extruder. The LCP particle sizeafter melt mixing and before the sheet extrusion should be not greaterthan about 30 μm, preferably, about 1-10 μm. In addition, in order toobtain a uniformly sized LCP fibers in the fluoropolymer matrix in thesheet formation step, use of a T-die or annular die for extrusion aftermelt mixing is preferred.

[0035] The aforementioned melt processible fluoropolymer and the LCP,preferably with a functional group-containing fluoropolymer in themixture (hereafter, the mixture may be called “fluoropolymer blend”) areused to prepare fluoropolymer sheet in which the LCP is in a fibrousstate, the fibers being oriented in the machine direction, that is, thedirection of the extrusion. This is achieved by extruding thefluoropolymer mixture into sheet form using a T-die or annular die.During this extrusion, the LCP particles dispersed in the fluoropolymermatrix are deformed into a fibrous form. In order to uniformly turn theminto fibers in the fluoropolymer matrix from the LCP dispersed phase inthe sheet extruding steps, the extrusion temperature should preferablybe at least about the melting point of the LCP used therein andpreferably no more than about 20° C. greater that the meltingtemperature of the LCP.

[0036] The diameters of the LCP fibers in the fluoropolymer matrix inthe melt processible fluoropolymer sheet extruded by a T-die or the likecan be controlled by the size of the particles or droplets of the LCPdispersed in the melt mixture before sheet extrusion and by the drawratio in the melt extrusion step (die lip clearance/thickness of thefilm or sheet produced). The smaller the size of the droplets ofdispersed LCP in the molten mixture before sheet extrusion, and thegreater the draw ratio, the smaller the diameter of the LCP fibers. Thedraw ratio should be at least about 5, preferably in the range of about10-200.

[0037] The extruded sheet thickness is about 10-1000 μm, preferablyabout 20-400 μm. At least 50 wt %, preferably 70 wt %, more preferably90 wt % of the LCP fiber should have a diameter of not more than about30 μm, preferably in the range of about 1-10 μm and have an aspect ratioof at least about 10, preferably at least about 20. The aspect ratio isdefined as the length of the fiber divided by the diameter of the fiberor if the fiber is not circular in cross section, its maximumcross-sectional dimension. When extruded sheet thickness is less thanabout 60 μm, the LCP fiber, rather than being round in cross section,tends to assume a ribbon-like cross section, i.e. an approximatelyrectangular cross section. In this case, the dimensions disclosed aboveshould be understood to refer to the greater dimension of the fibercross section, the longer side of the approximately rectangular crosssection.

[0038] The fluoropolymer laminates of this invention can be formed byusing an extruded sheet of the type described above in at least onelayer thereof. That is, the laminate may be comprised of one or two ormore layers of said extruded sheets and one or two or more layers ofmelt processible fluoropolymer sheets not containing fibrous LCP, orfrom multiple extruded sheets of the melt processible fluoropolymercontaining fibrous LCP. Further they may be constituted from one or twoor more sheets of said extruded sheets and one or two or more sheets ofpolymer layers other than melt processible fluoropolymer and havingcoefficients of linear expansion of about 6×10⁻⁵/° C. or less.

[0039] Manufacture of the laminates of this invention from a pluralityof the above extruded sheets is done by overlaying the multiple sheetsand bonding them with heat and pressure. Since the above-extruded sheethas the LCP fibers oriented mostly in the direction of draw (MD ormachine direction) there is substantial anisotropy in physicalproperties between the MD and TD (transverse direction). To reduce oreliminated anisotropy in physical properties of the laminate, twoextruded sheets are overlaid in such a way that the orientationdirections of the fibers of LCP are at approximately right angles (atwo-layer lamination). With three or more layers (multilayerlamination), the layers are overlaid at different angles so as to obtainas far as possible the same properties in all directions. The optimalarrangement for a laminate of N layers can be approximated by overlayingeach layer after the first so that its MD is +180°/N offset from thelayer below it. However, for minimum waste and to reduce the need totrim the laminate, it is often better to overlay the layers at rightangles, preferably alternating with each layer. A even number of layersare preferred to give a more isotropic laminate.

[0040] Lamination may be done with heated rolls or presses providingboth the heat and pressure to achieve the bonding of the sheetstogether, on a plurality of the above-extruded sheets. Thickness of thelaminate is controlled by adjusting roll or press clearance and/orpressure.

[0041] The lamination temperature should be at least equal to themelting temperature of the fluoropolymer, but below the melting point ofthe LCP. If the lamination temperature is higher than the melting pointof the LCP, the oriented LCP fibers in the extruded sheet will melt andwill lose fibrous structure, which is not desirable. If the laminationtemperature is below the melting point of the fluoropolymer it will bedifficult to obtain good adhesion between the extruded sheets.Therefore, the lamination temperature should be at least about 2-30° C.higher than the melting point of the fluoropolymer and in the range ofat least about 10° C. lower than the melting point of the liquidcrystalline polymer. According to this invention, laminates may be twolayer or multilayer in which extruded sheets are sequentially overlaidwith the orientation of the LCP fibers unlimitedly arranged as desired.However, for low shrinkage, multilayer, i.e. greater than two layer,laminates are preferred. In the multilayer laminate, it is preferredthat the extruded sheets be overlaid so as to result in a laminate thatis as nearly as possible isotropic in regards to physical properties.The laminate may include one or more melt processible fluoropolymersheets containing no LCP and these may be the top and/or bottom layer ofthe laminate. The sequencing of the extruded sheet and melt processiblefluoropolymer sheet may be freely varied. Although it will depend uponthe application, the laminate thickness may be about 20-2000 μm thick,preferably about 50-1000 μm thick.

[0042] The laminate will have the fibrous LCP oriented in a singledirection in each component extruded sheet, but adjusted in such a waythat the physical properties are balanced, that is as uniform aspossible in all directions. Therefore, the melt processiblefluoropolymer laminates of this invention can provide low coefficient oflinear expansion, low thermal shrinkage, and at the same time a hightensile modulus that could not be achieved with conventionalfluoropolymer sheets. Since fluoropolymer has a dielectric constantlower than the liquid crystalline polymer, the laminate will exhibit alower dielectric constant than would a pure LCP sheet (as disclosed forexample, in Kokai H10-34742).

[0043] The fluoropolymer laminates resulting from lamination of theabove-extruded sheets may have LCP fibers in areas close to the sheetsurface and streaks may sometimes appear in the sheet in the MD,resulting in thickness non-uniformity. Streaks or thicknessirregularities in the fluoropolymer sheet will make it more difficult touse as a circuit board material. In order to prevent surface defectscaused by such streaks and thickness non-uniformities, temperature andpressure may be controlled during lamination, or one may overlay a meltprocessible fluoropolymer sheet or a functional group-containingfluoropolymer sheet on one side or both sides of the fluoropolymerlaminates, followed by lamination. The melt processible fluoropolymersheets or functional group-containing fluoropolymer sheet for suchobjectives may be, for example, about 10-500 μm thick.

[0044] Furthermore, for improving the peel strength between thefluoropolymer laminate of this invention prepared by lamination of theabove type extruded sheets and copper foil, one may overlay afunctional-group-containing fluoropolymer sheet or a blend of an LCP anda functional-group-containing fluoropolymer sheet on one or both sidesof the fluoropolymer laminate and laminating. Thefunctional-group-containing fluoropolymer sheet or a blend of an LCP anda functional-group-containing fluoropolymer sheet used for the purposeshould be not more than about 200 μm, preferably not more than about 100μm thick.

[0045] As described above, the fluoropolymer laminate of this inventionmay be comprised of one or two or more extruded sheets of a meltprocessible fluoropolymer containing fibrous LCP and one or two or moresheets of polymer layers other than melt processible fluoropolymers andhaving coefficients of linear expansion of about 6×10⁻⁵/° C. or less,such polymer sheets thereby being isotropic. Use of these isotropicsheets such as biaxially stretched sheets having this low coefficient oflinear expansion in both (perpendicular) directions as the polymerlayers is advantageous in that this will facilitate formation of asubstantially isotropic fluoropolymer laminate with a minimal effect ofthe orientation directions of the fibrous LCP that constitute the aboveextruded sheets. The temperature of the lamination should be below themelting point of the isotropic LCP sheet so as to avoid melting the LCPand changing the properties of the LCP sheet.

[0046] The polymers used above should have coefficients of linearexpansion of about 6×10⁻⁵/° C. or less, preferably about 5×10⁻⁵/° C. orless, more preferably about 3×10⁻⁵/° C. or less. Such polymers include,for example, LCPs mentioned above as fibrous LCP materials, polysulfone,amorphous polyarylate, polyphenylene sulfide, polyether sulfone,polyetherimide, polyamideimide, polyetheretherketone, and polyimide.When this type of polymer sheet is used, it is preferred that it besandwiched between two layers of the fibrous LCP-containing meltprocessible fluoropolymer layers. In this case the polymer sheet layerthickness, although dependent on the application, may be, for example,about 10-2000 μm, preferably about 20-400 μm, with the overall laminatebeing for example about 20-2000 μm, preferably about 50-1000 μm thick.In such cases, use of the above type extruded sheet or afunctional-group-containing type fluoropolymer as a melt processiblefluoropolymer can enhance the adhesion to copper foil.

[0047] Another method for obtaining the fluoropolymer laminate accordingto this invention includes, instead of using the above extruded sheetscontaining fibrous LCP, using a fabric made from fiber of a meltprocessible fluoropolymer containing a fibrous LCP by methods such asweaving or knitting, or by techniques for making nonwoven fabrics. Inorder to prepare a melt processible fluoropolymer fiber containing LCPoriented in the fibrous state, one may use materials similar to thosecited above for extruded sheet, extruding under similar conditions butthrough dies, also known as spinnerets, suitable for fiber formation.For the details of such a process, see disclosures in Kokai 2001-88162(EP 1 086 987 A1) and 2001-181463 (U.S. patent application Publication2001/0006727). It is preferred that the fiber diameter to be about5-1000 μm, and that the LCP fibers have a diameter of not more than 30μm, preferably about 1-10 μm with an aspect ratio being preferably atleast about 40, preferably at least about 80. The fiber sheet shouldparticularly have a thickness of about 10-1000 μm, particularly about30-500 μm.

[0048] The fibrous LCP in the melt processible fluoropolymer fiber isoriented in the lengthwise direction or MD, i.e. along the fiber axis.The fibrous sheet resulting from converting the melt processiblefluoropolymer fiber to non-woven fabric, woven fabric, knitted fabric,or the like, has generally isotropic physical properties. Therefore, bylaminating melt processible fluoropolymer sheet or functionalgroup-containing fluoropolymer sheet to one side or both sides of such afiber sheet, one can obtain a preferred fluoropolymer laminate of thisinvention. In such a case, the laminate, like a laminate from extrudedsheet, may be made about 2-2000 μm, preferably about 50-1000 μm thick.For the manufacture of fibrous sheets such as woven fabric, non-wovenfabric, knitted fabric, or the like, from a melt processiblefluoropolymer fiber containing a fibrous LCP, known technologies can beused that are employed for generating fibrous sheets from common fibers.Examples of such technologies are weaving and knitting.

[0049] Any desired layer of the fluoropolymer laminated layers of thisinvention may be optionally formulated with additives. Such additivesinclude, for example, antioxidants, light stabilizers, antistaticagents, fluorescent whiteners, colorants, metal oxides such as silica,alumina, and titanium oxide; metal carbonates such as calcium carbonateand barium carbonate; metal sulfates such as calcium sulfate, and bariumsulfate; silicate salts such as talc, clay, mica, and glass; as well asinorganic fillers such as potassium titanate, calcium titanate, andglass fibers; and organic fillers such as carbon black, graphite, andcarbon fibers.

[0050] This invention provides fluoropolymer laminates of have a thermalshrinkage of not more than 1.5%, preferably not more than 1.2% at 250°C. and a dielectric constant at the frequency 1 GHz of not more thanabout 3.0, preferably in a range of about 2.1-2.9, more preferably in arange of about 2.1-2.6.

[0051] The difference in the thermal shrinkage at 250° C. between themachine and transverse directions should not be more than about 10%,preferably not be more than about 5%, more preferably about 0%.

EXAMPLES

[0052] LCP is Liquid Crystalline Polymer

[0053] Laminate properties are determined as follows:

[0054] (1) Thermal Shrinkage

[0055] Samples, 100 mm×10 mm, sample are cut out from the sheet orlaminate in both the MD and TD, and the length in the longer dimensionis measured using an optical microscope. Then, the samples are put intoa constant temperature circulating-air oven at 250° C. for 30 minutes,then cooled to room temperature, and remeasured. The thermal shrinkagefor each sample is determined using the equation below. Thedetermination calls for measuring three samples and averaging theresults to give the reported value. Thermal shrinkage=((length beforeheating−length after heating)/length before heating)×100.

[0056] (2) Dielectric Constant

[0057] Dielectric constant is measured using the three-plate circuitresonance method. This method is described in “Polymers For HighFrequency Applications”, Chap 5.4.4, CMC Press, Tokyo, 1999. Thefrequency is 1 GHz.

[0058] (3) Tensile Modulus

[0059] Tensile Modulus is measured according to ASTM D882 at a rate ofseparation of 50 mm/min.

[0060] (4) Peel Strength

[0061] A PFA laminate is laminated to a 0.1 mm thick copper foil using ahot plate press (temperature 325° C., pressure 3 MPa for 15 minutes toobtain a 1 cm wide peel test sample, which test piece is then testedaccording to IPC-TM-650 2.4.8, using the 180° peel test at the rate of50 mm/min. Peel strength (kg/cm) is measured. The IPC Test Manual 650 isavailable from IPC—Association Connecting Electronics Industries, 2215Sanders Rd., Northbrook Ill. 60062-6135, USA.

[0062] (5) Coefficient of Linear Expansion

[0063] Coefficient of linear expansion is measured with a SeikoInstruments Inc. TMA SS120. Temperature range is 25°-250° C.; scan rate5° C./min; Load 50 mN. Sample size 10 mm by 3 mm.

Example A

[0064] PFA (manufactured by Mitsui-DuPont Fluorochemicals Co., “PFA340”; melting point 308° C., melt flow rate (372° C., 5000 g weight), 14g/10 min) and LCP (manufactured by DuPont Company, Zenite®, 7000,melting point 350° C.) are thoroughly dried and then melt blended at365° C. in a twin screw extruder, along with a terpolymer oftetrafluoroethylene, perfluoro(propyl vinyl ether) (PPVE), andCF₂═CF[OCF₂CF(CF₃)]OCF₂CF₂CH₂OH, (PPVE content 3.7% by weight, 1.1% byweight of the hydroxy-containing monomer, melt flow rate 15 g/10 min) ascompatibilizing agent, (fluoropolymer temperature 365° C.) to obtain afluoropolymer blend. The LCP content of the blend is 20% by weight andthe compatibilizing agent content is 2.5% by weight.

[0065] The pelletized fluoropolymer mixture from the above is melted ina 30 mm single screw extruder and extruded using a T-die (lip length 200mm, lip clearance (die opening) 2 mm, die temperature 365° C.) togenerate a 100 μm thick fluoropolymer sheet, S1, which contains fibrousLCP oriented in the direction of extrusion, i.e. the MD.

Examples B and C

[0066] Example A is repeated except that the LCP content is 10% byweight (in Example B), and 3% by weight (in Example C) to givefluoropolymer sheet samples, S2 and S3. The resultant fluoropolymersheets are then cleaved in liquid nitrogen at an angle perpendicular tothe direction in which the fibrous LCP oriented, followed by observationunder a scanning electron microscope (SEM). The results are shown inFIGS. 1 and 2.

Examples 1-3

[0067] Two fluoropolymer sheets of sample S1 from Example A areoverlaid, arranging two sheets so as to have the LCP fibers oriented atright angles, followed by lamination on a hot plate (temperature 325°C., pressure 3 MPa), followed by cooling to obtain a 180 μm thickfluoropolymer laminate, which is designated sample S4. This is repeatedusing samples S2 and S3 to give samples S5 and S6 respectively.

Example 4

[0068] A fluoropolymer mixture having the same composition as that ofExample C that has been melt blended by a twin screw extruder is spunusing a 30 mm twin screw extruder (Length/Diameter: 25) through aspinneret having 6 orifices with the orifice diameter of 2.8 mm at aspinning temperature of 365° C. and taken up by a take-up roller at arate of 300 m/min to give a monofilament (diameter 80 μm), which is thenplain woven at a density of 45 threads/25 mm into a cloth sheet (160 μmthick). A 50 μm thick functional-group containing PFA (thecompatibilizer agent used in Example A) sheet is prepared using the samehot plate press used in Example A, followed by overlaying functionalgroup-containing PFA sheets, one on each side of the cloth sheet,followed by lamination in a hot plate press (temperature 325° C.,pressure 3 MPa) and cooling to obtain a 230 μm thick laminate of thefunctional group-containing PFA impregnated into the cloth sheet,designated as sample S7.

Example 5

[0069] Two fluoropolymer sheets prepared by the procedure of Example Bare overlaid in such a way that the LCP fibers are oriented at rightangles. On each side of this pair of sheets is overlaid functionalgroup-containing PFA sheets prepared by the procedure of Example 4 togive the laminate structure: functional group-containing PFAsheet/fluoropolymer sheet/fluoropolymer sheet/functionalgroup-containing PFA sheet. This combination is laminated in a hot platepress (temperature 325° C., pressure 3 MPa), followed by cooling to givea 250 μm thick fluoropolymer laminate, sample S8.

Example 6

[0070] A fluoropolymer mixture having the same composition as that ofExample B is extruded from a 30 mm single screw extruder fitted with aT-die (lip length 200 mm, lip clearance 2 mm, die temperature 365° C.)to generate a 25 μm thick fluoropolymer sheet containing fibrous LCP.Six pieces of this fluoropolymer sheet are overlaid so that theorientation directions of the fibrous LCP cross are at right angles,laminated using a hotplate press (temperature 325° C., pressure 3 MPa),and allowed to cool, giving a 150 μm thick fluoropolymer laminatedesignated sample S9.

Example 7

[0071] Fluoropolymer sheets, 25 μm thick, prepared by the procedure ofExample 6 are overlaid on the top and bottom sides of a 50 μm thick LCP(Zenite® 7000) sheet, which is biaxially stretched in such a way thatthe orientation directions of the fibrous LCP are as near as possiblythe same. This is difficult because of the problem of stretching LCP,which is discussed in the Background of the Invention. The combinedsheets are laminated on a hot plate press (temperature 325° C., pressure3 MPa), and allowed to cool, resulting in a 100 μm thick laminatedesignated sample S10.

Example 8

[0072] A 1 mm thick laminate prepared by laminating the fluoropolymersheets made by the procedure of Example A is laminated to copper foilusing a hot plate press (temperature 325° C., pressure 3 MPa) to obtaina sample for peel testing.

Example 9

[0073] A 1 mm thick fluoropolymer laminate obtained by the procedure ofExample 6, except for decreasing the amount of the LCP to 10% by weight,and increasing the functional-group containing PFA to 10% by weight, islaminated to copper foil using a hot plate press thereby obtaining apeel test sample.

Example 10

[0074] A 1 mm thick laminate prepared by laminating the fluoropolymersheets prepared by the procedure of Example C is laminated to copperfoil using a hot plate press to obtain a peel test sample.

Comparative Example 1

[0075] PFA fluoropolymer (PFA 340) is compression molded into sheetusing a hot plate press (temperature 350° C., pressure 6 MPa) and cooledto give a 200 μm thick PFA sheet, sample R1.

Comparative Example 2

[0076] LCP (Zenite® 7000) is compression molded into sheet form using ahot plate press (temperature 360° C.) and cooled to give a 200 μm thicksheet, sample R2.

Comparative Example 3

[0077] A 1 mm thick laminate obtained by laminating PFA (PFA 340) sheetsof Comparative Example 1 is laminated to copper foil in a hot platepress to obtain a peel test sample.

[0078] The physical properties of the melt processible fluoropolymersheets and laminates prepared above are measured and the results aresummarized in Tables 1 and 2 and FIGS. 1 and 2. Since the samples S1, S2and S3 have their LCP fibers oriented in one direction withconsequential anisotropy in physical properties, their physicalproperties are measured in both the MD and TD. Since samples S4-S6 andS8-S9 have their liquid crystalline fibers oriented so that the fibersin the top fluoropolymer sheet are at right angles to the fibers in thebottom sheet, and since Sample 10 is a biaxially stretched isotropic LCPsheet, both MD and TD properties are measured, but no difference isfound between the two directions. Therefore only the results measured inone direction (thermal shrinkage and tensile modulus) are summarized inTable 1. The results of peel strength testing of these pieces aresummarized in Table 2. TABLE 1 Thermal Tensile Shrinkage % DielectricModulus (MPa) Sample MD TD Constant MD TD No. Example A 0.2 1.5 2.6 3500700 S1 Example B 0.3 3.5 2.4 2060 560 S2 Example C 2.0 3.8 2.2 490 440S3 Example 1 0.8 2.5 1740 S4 Example 2 1.1 2.3 980 S5 Example 3 2.1 2.1550 S6 Example 4 1.4 2.4 720 S7 Example 5 1.3 2.2 690 S8 Example 6 0.62.2 995 S9 Example 7 0.5 2.5 2500  S10 Comp. Ex 1 4.1 2.1 475 R1 Comp.Ex 2 Not more than 0.1% 3.0 Not measured R2

[0079] TABLE 2 Composition (% by weight) Compatibilizing LiquidCrystalline Peel Strength PFA Agent Polymer (kg/cm) Example 8 77.5 2.520 2.8 Example 9 80 10 10 3.6 Example 10 94.5 2.5 3 1.7 Comp. Ex 3 100 00 0.8

[0080] Table 1 shows that in the fluoropolymer sheets S1, S2 and S3,obtained by extrusion through a T-die (Examples A-C), improvements areobserved in thermal shrinkage and tensile modulus with increasing amountof the liquid crystalline polymer. However, since the LCP is oriented inone direction, there is anisotropy in the physical properties. FIGS. 1and 2 show that sample S2 (Example B) with a 10% by weight LCPincorporated has fibrous LCP throughout the sheet cross-section while asample S3 (Example C) with a 3% by weight of the LCP has the minimumamount of fibrous LCP. Therefore, the blend ratio of the LCP, whichdepends on the T-die extrusion conditions, is in the range of about3-25% by weight, preferably about 4-25% by weight. Blendingfluoropolymer with LCP increases the dielectric constant somewhat, buteven sample S1 (Example A) having a 20% by weight of LCP has adielectric constant of only 2.6, still suitable for a circuit boardmaterial for high frequency use.

[0081] Laminate samples (Examples 1-3) obtained by laying twoT-die-extruded fluoropolymer sheets one over the other so as to have theLCP fibers oriented at right angles, thereby reducing anisotropy in thephysical properties of the fluoropolymer sheet samples, followed by ahot plate press lamination also show improved thermal shrinkage andtensile modulus with an increase in the blend ratio of the liquidcrystalline polymer. Essentially no difference in physical properties isobserved between the MD and TD. Example 1 shows that it is possible toreduce thermal shrinkage to 1% or less by increasing the amount of theLCP to 20% by weight or higher. A sample obtained by replacing the T-dieextruded fluoropolymer sheet with a fluoropolymer cloth sheet (Example4) shows improved thermal shrinkage and tensile modulus relative to apure fluoropolymer sheet (Comparative Example 1).

[0082] Laminate S8 (Example 5) obtained by overlaying fluoropolymersheet and functional group-containing PFA sheet in this order:functional group-containing PFA sheet/fluoropolymer sheet/fluoropolymersheet/functional group-containing PFA sheet has thermal shrinkage andtensile modulus inferior to Example 2 because of the two functionalgroup-containing PFA sheets without LCP component, but it has a superiordielectric characteristics. As shown in FIG. 1, the fluoropolymer sheethaving LCP oriented in the fibrous state has the LCP fiber present evenin the area close to the sheet surface so that sometimes streaks appearin the sheet MD with thickness non-uniformity. Streaks and thicknessnon-uniformity in the fluoropolymer sheet would make it difficult to usesuch a material for circuit board. A laminate as in Example 5 iseffective for overcoming the streaked surface state due to such streaksand thickness non-uniformity. Since Example 5 hasfunctional-group-containing PFA sheets on both sides, it is expected toprovide improved peel strength to copper foil.

[0083] The sample of Example 6 (X/Y/X/Y/X/Y, X=MD, Y=TD) prepared byhaving six fluoropolymer sheets, in which the LCP is oriented in thefibrous state, crossed at right angles, in place of the product from a2-layer lamination (Example 2, X/Y directions), of the same overallcomposition, involves more cancellation of the orientation directions inthe laminate, so that its thermal shrinkage is less than that of Example2. Therefore, from the standpoint of achieving isotropic physicalproperties, the fluoropolymer laminate is preferably a multi-layeredlaminate having 4, 6, 8 layers or more, rather than a 2-layer laminate.S10 (Example 7), the laminate prepared from fluoropolymer sheets inwhich LCP is oriented in the fibrous state on either side of an LCPsheet prepared, by biaxial stretching method exhibits improved thermalshrinkage and tensile modulus by virtue of having the LCP sheet.

[0084] Peel strength test results summarized in Table 2 show that PFAsheet bonded to copper foil (Comparative Example 3) has poor peelstrength. However, samples in which a compatibilizing agent and LCP areblended show improved peel strength. In particular, Example 7 shows asynergistic effect of the compatibilizing agent and LCP on the peelstrength. Though both LCP and compatibilizer beneficially affectadhesion, as stated above, excessive LCP can lead to “pockets” of LCP inthe blends with deleterious effects on extrusion and laminate quality.Excessive amounts of compatibilizer can decrease the heat stability ofthe laminate. Therefore, the amounts LCP and compatibilizer and theirratios should be chosen to balance the beneficial with the deleteriouseffects of these ingredients.

Example 11

[0085] Two 25 μm thick fluoropolymer sheets, each containing LCPoriented in a fibrous state, prepared by the procedure of Example 6 areoverlaid on the top and bottom sides of a 50 μm thick sheet of polyamide(Kapton® H manufactured by DuPont-Toray Co. Ltd.) having a coefficientof linear expansion of 2.7×10⁻⁵/° C. in perpendicular directions. Theorientation directions of the sheets are the same direction in theoverlaid assemblage. The assemblage is hot pressed at 325° C., which isabove the melting point of the fluoropolymer, but less than the meltingpoint of the polyimide, at a pressure of 3 MPa, and allowed to cool,resulting in the bonding of the fluoropolymer sheets to each side of thepolyimide sheet to form a laminate thereof 100 μm thick The resultantlaminate exhibits a thermal shrinkage of 0.6%, a dielectric constant of2.9, and a tensile modulus of 1850 MPa

[0086] The present invention provides fluoropolymer laminates havingisotropic properties. For example, an embodiment in which multiplefluoropolymer sheets containing fibrous LCP in the melt processiblefluoropolymer are laminated, despite having the fibrous LCP oriented inone direction in a single extruded sheet, makes it possible to laminatein such a way as to compensate for their orientation directions, thelaminate thereby becoming isotropic as regards physical properties.Therefore, the invention provides fluoropolymer laminate having a lowlinear coefficient of expansion and low thermal shrinkage that can notbe achieved with conventional fluoropolymer sheets, the laminates alsohaving elevated tensile modulus and low dielectric constant.

[0087] A fluoropolymer laminate of this invention having such propertiesis suitable for circuit board material. It is also expected to findapplications other than circuit boards such as in insulating sheetmaterials for transformers and motors, heat resistant sheets, prepregsubstrates, and in the packaging material area.

What is claimed is:
 1. Fluoropolymer laminate comprising meltprocessible fluoropolymer layers wherein at least one layer thereof is afluoropolymer sheet layer in which an LCP is oriented in the fibrousstate in the melt processible fluoropolymer.
 2. The laminate as setforth in claim 1, wherein said laminate comprises at least twofluoropolymer sheet layers having an LCP oriented in the fibrous statein the melt processible fluoropolymer, and wherein at least two layersthereof have fibrous LCP whose orientation is in directions differentfrom each other.
 3. The laminate as set forth in claim 1, wherein thefluoropolymer sheet layer having an LCP oriented in the fibrous state inthe melt processible fluoropolymer is a fibrous sheet layer selectedfrom a woven fabric, a non-woven fabric, and a knitted fabric of meltprocessible fluoropolymer fibers containing the LCP oriented in thefibrous state.
 4. The laminate as set forth in claim 1, wherein thefluoropolymer sheet layer having an LCP oriented in the fibrous state inthe melt processible fluoropolymer contains the LCP in a range of about3-30% by weight thereof.
 5. The laminate as set forth in claim 1,wherein at least one of said layers is a melt processible fluoropolymersheet containing no fibrous LCP laminated to at least one side of saidat least one fluoropolymer sheet layer in which the LCP is oriented inthe fibrous state.
 6. The laminate as set forth in claim 1, wherein atleast part of the melt processible fluoropolymer is afunctional-group-containing fluoropolymer.
 7. The laminate as set forthin claim 1, wherein at least one of said layers is a polymer layer witha coefficient of linear expansion of about 6×10⁻⁵/° C. or less laminatedto at least one side of said at least one fluoropolymer sheet layer inwhich the LCP is oriented in the fibrous state.
 8. The laminate as setforth in claim 7, wherein the fluoropolymer sheet layer in which an LCPis oriented in the fibrous state in the melt processible fluoropolymeris laminated to at least one side of the polymer layer with acoefficient of linear expansion of about 3×10⁻⁵/° C. or less.
 9. Thelaminate as set forth in claim 1, and additionally copper cladding onone or both sides of said laminate.
 10. The laminate as set forth inclaim 7, wherein said fluoropolymer sheet layer in which an LCP isoriented in the fibrous state in a melt processible fluoropolymer islaminated to both sides of said polymer layer with a coefficient oflinear expansion of about 6×10⁻⁵/° C. or less, and wherein theorientation direction of the fibrous LCP in each said fluoropolymersheet layers is the same or different.
 11. The laminate as set forth inclaim 1, wherein said laminate has a thermal shrinkage at 250° C. of notmore than about 1.5% and a dielectric constant at a frequency of 1 GHzof not more than about 3.0.
 12. A process for the manufacture offluoropolymer laminate, comprising melt mixing a melt processiblefluoropolymer with an LCP having a melting point of at least about 15°C. higher than that of said melt processible fluoropolymer; extrudingthe resultant melt mixture in the form of a sheet in which the LCP isoriented in the fibrous state in the melt processible fluoropolymer inthe direction of said extruding; overlaying multiple sheets obtainedfrom said extruding in such a way that at least two sheets will havetheir respective LCP oriented in the fibrous state oriented indifferentdirections; and laminating said multiple sheets together.
 13. Theprocess for the manufacture of fluoropolymer laminate, comprisingoverlaying a melt processible fluoropolymer sheet containing no fibrousLCP on at least one side of a fibrous sheet selected from a wovenfabric, a non-woven fabric, or a knitted fabric of fluoropolymer fibershaving an LCP oriented in the fibrous state in the melt processiblefluoropolymer in the fiber direction; and laminating said fluoropolymersheet and said fibrous sheet together.
 14. The process for themanufacture of a fluoropolymer laminate, comprising melt mixing a meltprocessible fluoropolymer with an LCP having a melting point of at leastabout 15° C. higher than that of said melt processible fluoropolymer;extruding the resultant melt mixture into the formation of a sheet inwhich the LCP is oriented in the fibrous state in the melt processiblefluoropolymer in the direction of said extruding; overlaying at leastone sheet obtained from said extruding on at least one side of aisotropic polymer sheet with a coefficient of linear expansion of about6×10⁻⁵/° C. or less; and laminating said fluoropolymer sheet and saidpolymer sheet together.